Heat exchanger devices produced with heat exchanger cores or core assemblies of this kind are needed for example in compressed air installations for extracting the moisture from compressed air created by means of a compressor and under a pressure of e.g. 25 bar, in order to make the air suitable for critical applications, such as in the foodstuffs and paper industries or the medical field. The drying of the air is effected in that the heated air arriving from the compressor is passed—after passage through an after-cooler—through a device which includes an air/air and a coolant/air heat exchanger. While the air/air heat exchanger is mostly manufactured in the form of a plate heat exchanger of conventional construction, the coolant/air heat exchanger mostly consists of a combined tube/plate heat exchanger with a core which has air passages and intervening coolant passages formed by plates and bars holding these spaced apart. The coolant passages each consist for example of tubes of round or square cross-section arranged between two plates, with straight sections and diverting sections connecting these in serpentine or meandering form (EP 0 521 298 A2).
The serpentine or meandering disposition of the tubes for the coolant gives the advantage that the coolant is circulated through heat exchanger core instead of, as usual, flooding the core, i.e. the coolant circulates through the straight tube sections one after the other and not in parallel. However, a disadvantage of this construction is that unused spaces result between the individual tube sections, which results in the length of the coolant/air beat exchanger core mostly having to be made greater than the length of the air/air heat exchanger grid. Moreover the curved diverting sections lie as a rule outside the space occupied by the actual core, so that they do not participate in the heat exchange.
In addition it has already been proposed (likewise EP 0 521 298 A2) to replace the passages through which the coolant flows by tube and diverting sections, produced in the conventional plate construction in which the tube and diverting sections are bounded by conventional bars running in transverse and longitudinal directions, arranged between the plates. Circulation through the core is indeed likewise achieved with such an arrangement. However, a disadvantage is that either comparatively thick bars have to be provided, in order to provide sufficiently large soldering areas for stable soldered joints, so that reduced flow cross-sections are obtained for given overall dimensions of the core, or narrow bars have to be used, which favour good flow cross-sections, but comparatively small soldering surfaces have to be taken into account. A consequence of this is that overall a compromise always has to be found between the cross-section of the coolant passages and the size of the soldering areas and the strength of the heat exchanger core which can be obtained thereby. In view of the fact that for many applications burst pressures for the core of 100 bar and more have to be provided, it follows that the overall dimensions of the heat exchanger core are affected substantially by the thickness of the bars bounding the channels.
In the ligth of the above it is an object of this invention of so forming the coolant/air heat exchanger assembly of the kind above specified that it can be produced with the required strength using cost effective manufacturing processes.
A further object of this invention is to design the heat exchanger core assembly mentioned above such that it can be manufactured without remarkable problems by means of usual soldering.
Yet another object of this invention is to provide the core assembly mentioned above with comparatively large flow cross-sections for the coolant with given overall dimensions.